One of the most widely used microwave antennas for radar is the parabolic reflector, which is a device that radiates and focuses electromagnetic energy by use of the shape of the curve of a parabola. The typical design of a radar system with a parabolic reflector involves an individual radiator that transmits electromagnetic energy toward the reflector where it is then directed toward a target. Reflected energy from the target returns to the parabolic reflector where it is focused onto an individual receiver. Data processing equipment then interprets the signal. The design of this radar system is such that the transmitter, receiver, data processing equipment, and the parabolic reflector are all individual and distinct elements of the radar unit. As a by-product of radar operation, each element is heated. Because in the parabolic reflector radar system design the elements are sufficiently separated, cooling, especially of the transmitter, may be accomplished fairly easily.
While this radar design is effective, the time and mechanical stress of physically orienting the parabolic dish for direction is a disadvantage. Furthermore, mechanical scanning is required and typical scan rates are in the range of 60-120 azimuth degrees per second. For detection of a small number of objects the parabolic dish antenna is
2 53,716 adequate but in order to track a large number of objects a different type of antenna is required
An electronically steered phased array radar utilizes an antenna that consists of a large number of fixed individual radiators suitably spaced over a flat surface and electronically fed so that a beam is projected in a desired location. The beam can be made to scan by changing the relative phases of the signal and each transmitter. Although the electronically steered phased array radar system is complex, and not capable of the same precision as the parabolic dish, beam steering is essentially inertialess and this type of antenna is ideal when it is necessary to shift the beam rapidly from one position in space to another, or where it is required to obtain information about many targets at a flexible, rapid data rate.
Unlike the parabolic dish antenna, with an electronically steered phased array system the antenna elements, the transmitters, the receivers, and the data processing portions of the radar are often designed as a unit. Also unlike the parabolic dish antenna, heat accumulation caused by the concentration of these elements into one unit becomes a problem and adequate heat dissipation is imperative for proper radar performance.
As mentioned in an array antenna radar system, the antenna elements, transmitter, receiver, and data processing electronics typically are contained in a single unit, which will be referred to as a T/R (transmitter/receiver) module. On the face of each module is an individual antenna used to transmit and receive signals. FIG. 1A shows individual antennae 10 with their respective T/R modules 12 on a portion of an array antenna, which may consist of anywhere from several to thousands of T/R modules 12 with the maximum number limited only by practical considerations. Note this view is from the back of the antenna and the front radiating face side is generally planar, as shown in FIG. 1B. Furthermore the individual antenna 10 are cylindrical nubs at the end of a T/R module 12 and the nubs are frictionally inserted into holes of smaller diameter on the locating plate 14 until flush with the locating plate 14. Some applications require up to 2,000 T/R modules 12 per array. These T/R modules 12 are typically small and closely spaced and usually located in a grid with equal spacing between modules.
During operation these modules generate relatively large amounts of heat, and consequently cooling becomes a critical factor. Note that the overheating of components is the primary cause of failure for radar systems. Present phased array designs utilize a very accurate front face locating plate 14 which maintains the module centers within 0.002 inches of each other at any location. The method of cooling must in no way interfere with the location accuracy of the modules on the plate. With past developments in the field of electronics, the T/R module sizes have been decreasing but the power requirements have not and consequently it is now possible to construct a radar system having a greater concentration of T/R modules. One result of the increased concentration of modules on an antenna and the greater heat accumulation within each T/R module is an increased heat buildup within the modules. An effective cooling method that addresses this increased heat accumulation within each module is very important to insure proper radar performance. The current cooling methods, although adequate for earlier antenna designs, may not be effective for cooling the more closely spaced smaller T/R modules.
One method of cooling, shown in FIG. 2, is utilized for a transmitter element 20 found in the electronically steered antenna. This method utilizes an element 20 configured with a tapered bottom compatible with similarly tapered receiving holes in a mating plate 22 such that conduction from the element 20 to the plate 22 would be sufficient to cool the element. This design is limited to phased array antenna transmitter elements generating a relatively small amount of heat.
Active phased array antennas, on the other hand, generate significantly larger amounts of heat. For maximum heat transfer from T/R modules on a phased array antenna of this type there must be high thermal conductivity between the T/R modules and a heat sink. Ideally a coolant fluid should be directly against the module but since the modules are not designed to be water-tight, this option is not possible. In lieu of direct contact, any means of transporting coolant fluid past a plurality of modules, such as through a conduit, may be used but must not impart any weight load onto the modules that would be sufficient to displace the precise alignment of the modules. Any conduit must be relatively stiff so that it could be structurally supported from the frame used to support the modules. On the other hand the conduit must adequately contact the module to encourage heat transfer. A relatively stiff conduit, if put in contact against a module, absent the introduction of some sort of intermediate conductor such as grease, must be precisely fitted or pressed against the module with an excessive force sufficient to deform the conduit around the module so that adequate surface contact exists. In all probability this deformation force of the stiff conduit would displace the module enough to result in misalignment of the module.
FIG. 3 shows a more effective heat transfer configuration where a semicircular slot 30 is designed on opposite faces of a T/R module 32 such that two adjacent modules would form a circular channel into which a heat pipe 34 is inserted for a passage means of heat dissipation. The heat pipe 34 is then used to transfer heat into a nearby heat sink. This method is cumbersome because it requires the application of grease between the heat pipes 34 and their contact surface with the T/R modules 32. Proper heat conduction depends on the distribution of the grease across the module interface. Furthermore, the custom-made heat pipes 34 are difficult to manufacture and vary in their thermal performance as a function of attitude, which is related to gravitational orientation.
Another cooling method is shown in Japanese Patent No. O22O954 dated May 11, 1985 entitled "Cooling Device For Integrated Circuit Element". This teaches improved cooling efficiency of integrated circuits using elastic cooling pipes which are bonded to a heat dissipating plate mounted on the IC substrate. The pressure of the cooling fluid causes the elastic pipes to expand and contact the upper surface of the IC chip. With the elastic pipe firmly against the IC chip, conduction from the IC chip to the cooling fluid is maximized. While this cooling technique is very effective, the arrangement of a cooling pipe mounted to a surface that is an integral part of the IC element present coupling problems when a series of IC modules exist. Furthermore, this method would not be effective if the elastic pipes required any structural support other than provided by the IC chip.
Another prior art design teaches an apparatus for cooling T/R modules by forcing a liquid coolant under pressure through a flat narrow conduit formed with two rectangular-shaped thin wall metal sheets sealed at their edges against two spacers and pressurized through the open ends. This conduit is placed between adjacent rows of T/R modules such that fluid pressure causes the metal sheets to deflect and contact the T/R modules, thereby cooling the T/R modules. This apparatus, because the metal may deform only until the metal sheet is taut, must be precisely fabricated to maximize contact with the modules. Even with precise fabrication, the heat transfer capability of the apparatus may be greatly reduced if the location of the T/R modules is slightly offset from the metal sheet, since the metal sheet will not stretch to meet the module. Overall, the effectiveness of this apparatus is highly dependent on the precise placement of the apparatus adjacent to the T/R modules.
An object of this invention is to provide a device for dissipating the heat generated from phased array antenna modules.
Another object of this invention is to provide sufficient contact between the coolant tube and the module without forcing the tube against the module causing deformation of the tube wall and unacceptable displacement of the module. The cooling device must be self-supporting and in no way interfere with the module location or with the module installation.
A further object of this invention is to provide a cooling device that is not absolutely dependent on the precise T/R module location so that the cooling device may be installed using large tolerances.